Synthesis, crystal structure, and electrochemical properties of hollandite-type K0.008TiO2

A single-phase specimen of hollandite-type K0.008TiO2 was synthesized by the ion extraction method using aqua regia treatment. Rietveld refinement from X-ray powder diffraction data for K0.008TiO2 showed it to have the hollandite-type structure (tetragonal; space group I4/m; a = 10.1631(6) Å and c = 2.9639(2) Å; Z = 8). The K0.008TiO2 specimen worked as a rechargeable electrode material. An initial capacity of 161 mAh/g (cut-off voltage: 1.0 V) could be achieved, and the reversible capacity after 50 cycles was 147 mAh/g. After lithium insertion–deinsertion cycling tests, the hollandite structure was still retained without structure collapse.